Technique for chemical mechanical polishing silicon

Abstract

Chemical mechanical polishing of a silicon layer, such as a polycrystalline silicon, is improved by initially chemical mechanically polishing the silicon layer with an oxide-polishing slurry. Then the silicon layer is chemical mechanically polished with a silicon-polishing slurry until the substrate is planarized.

What is claimed is:  
     
         1 . A method of polishing a silicon layer on a substrate, comprising: 
 (a) chemical mechanically polishing the silicon layer with an oxide-polishing slurry to remove any native oxides; and    (b) chemical mechanically polishing the silicon layer with a silicon-polishing slurry.    
     
     
         2 . The method of    claim 1   , wherein the silicon layer is polished until an underlying layer is exposed.  
     
     
         3 . The method of    claim 1   , wherein the silicon layer is polished until it is planarized.  
     
     
         4 . The method of    claim 1   , wherein step (a) and at least a portion of step (b) are performed at the same polishing station.  
     
     
         5 . The method of    claim 4   , wherein step (b) comprises distributing the oxide-polishing slurry onto a polishing pad at the polishing station before the substrate is brought into contact with the polishing pad.  
     
     
         6 . The method of    claim 4   , wherein step (b) comprises distributing the oxide-polishing slurry onto a polishing pad at the polishing station as the substrate is brought into contact with the polishing pad.  
     
     
         7 . The method of    claim 4   , wherein step (b) comprises distributing the oxide-polishing slurry onto a polishing pad at the polishing station after the substrate is brought into contact with the polishing pad.  
     
     
         8 . The method of    claim 1   , wherein distribution of the oxide-polishing slurry is stopped before distribution of the silicon-polishing slurry starts.  
     
     
         9 . The method of    claim 1   , wherein distribution of the oxide-polishing slurry is stopped as distribution of the silicon-polishing slurry starts.  
     
     
         10 . The method of    claim 1   , wherein distribution of the oxide-polishing slurry is stopped after distribution of the silicon-polishing slurry starts.  
     
     
         11 . The method of    claim 1   , wherein step (b) is performed at a plurality of polishing stations.  
     
     
         12 . The method of    claim 1   , further comprising buffing the substrate with a buffing solution after step (b).  
     
     
         13 . The method of    claim 1   , wherein the silicon layer is polycrystalline silicon.  
     
     
         14 . The method of    claim 13   , wherein the silicon-polishing slurry is a polycrystalline silicon-polishing slurry.  
     
     
         15 . The method of    claim 1   , wherein the silicon layer is amorphous silicon.  
     
     
         16 . The method of    claim 15   , wherein the silicon-polishing slurry is an amorphous silicon-polishing slurry.  
     
     
         17 . The method of    claim 1   , wherein the silicon layer is single crystalline silicon.  
     
     
         18 . The method of    claim 17   , wherein the silicon-polishing slurry is a single crystalline silicon-polishing slurry.  
     
     
         19 . The method of    claim 1   , wherein the silicon-polishing slurry has a selectivity of at least 1:50.  
     
     
         20 . The method of    claim 1   , wherein step (a) lasts for less than about ten seconds.  
     
     
         21 . The method of    claim 20   , wherein step (a) lasts for about three to five seconds.  
     
     
         22 . A method of planarizing a substrate, comprising: 
 (a) forming a silicon layer on a non-planar surface of the substrate;    (b) supplying an oxide-polishing slurry to a surface of a polishing pad;    (c) bringing the substrate into contact with the polishing pad;    (d) briefly chemical mechanical polishing the substrate with the oxide-polishing slurry to remove a native oxide layer from a surface of the silicon layer;    (e) after the substrate contacts the polishing pad, supplying a silicon-polishing slurry to the polishing pad; and    (f) chemical mechanical polishing the substrate with the silicon-polishing slurry until the silicon layer is substantially planarized.    
     
     
         23 . The method of    claim 22   , wherein the silicon layer is polycrystalline silicon and the silicon polishing slurry is a polycrystalline silicon polishing slurry.  
     
     
         24 . The method of    claim 22   , wherein the silicon layer is amorphous silicon and the silicon polishing slurry is an amorphous silicon polishing slurry.  
     
     
         25 . The method of    claim 22   , wherein the silicon layer is single crystalline silicon and the silicon polishing slurry is a single crystalline silicon polishing slurry.  
     
     
         26 . The method of    claim 22   , further comprising polishing the silicon layer at a second polishing pad with a second silicon-polishing slurry until the non-planar surface is exposed.  
     
     
         27 . The method of    claim 22   , further comprising stopping the supply of oxide-polishing slurry to the polishing pad surface before the silicon-polishing slurry is supplied to the polishing pad.  
     
     
         28 . The method of    claim 22   , wherein the silicon-polishing slurry is supplied to the polishing pad after the substrate has been in contact with the polishing pad for less than about ten seconds.  
     
     
         29 . The method of    claim 22   , wherein the substrate is chemical mechanically polished with the oxide-polishing slurry for less than about ten seconds.  
     
     
         30 . The method of    claim 29   , wherein the substrate is chemical mechanically polished with the oxide-polishing slurry for about three to five seconds.  
     
     
         31 . A method of polishing a silicon layer on a substrate, comprising: 
 (a) chemical mechanical polishing the silicon layer with an oxide-polishing slurry to remove a native oxide layer;    (b) chemical mechanical polishing the silicon layer with a silicon-polishing slurry until the silicon layer is substantially planarized; and    (c) stopping step (b) before the silicon layer is substantially planarized.    
     
     
         32 . A method of polishing a silicon layer on a substrate, comprising: 
 (a) chemical mechanical polishing the silicon layer with an oxide-polishing slurry to remove a native oxide layer;    (b) chemical mechanical polishing the silicon layer with a silicon-polishing slurry until an underlying non-planar surface is exposed; and    (c) stopping step (b) before the underlying non-planar surface is exposed.